Molecular detection of the index case of a subclinical Salmonella Kentucky epidemic on a dairy farm

Abstract

Salmonella enterica commonly colonizes the intestinal tract of cattle and is a leading cause of foodborne illness. A previously described investigation into the prevalence of S. enterica on a dairy farm revealed an 8-year-long asymptomatic S. enterica epidemic caused by serotypes Cerro and Kentucky in the lactating herd. To investigate the source of the S. Kentucky strains, the genomes of two S. Kentucky isolates were sequenced; one collected prior to the epidemic (2004) and one collected during the epidemic (2010). Comparative genomic analysis demonstrated significant polymorphisms between the two strains. PCR primers targeting unique and strain-specific regions were developed, and screening of the archived isolates identified the index case of the asymptomatic S. Kentucky epidemic as a heifer that was raised off-site and transported onto the study farm in 2005. Analysis of isolates collected from all heifers brought onto the farm demonstrated frequent re-introduction of clones of the epidemic strain suggesting transmission of pathogens between farms might occur repeatedly.

Genomic and Evolutionary Analysis of Two Salmonella enterica Serovar Kentucky Sequence Types Isolated from Bovine and Poultry Sources in North America

“…Salmonella Kentucky isolates from dairy cows were recovered from previously collected National Animal Health Monitoring System (NAHMS) samples as well as an eight-year dairy farm monitoring program conducted in south-central Pennsylvania [ 3 ][ 19 ] (two poultry-associated isolates were supplied by S. Parveen). Isolates were serogrouped following the methods of Herrera-Leon et al [ 20 ]and Karns et al [ 21 ]and serotypes were identified by National Veterinary Services Laboratories (NVSL; Ames, IA).…”

Salmonella enterica serovar Kentucky recovered from human clinical cases in Maryland, USA (2011–2015)

“…Based on the available data in the S. enterica multilocus sequence type (MLST) database, two sequence types (ST), ST152 and ST198, are among the most frequently isolated and characterized of the known S. Kentucky STs (Alikhan, Zhou, Sergeant, & Achtman, ). ST152 is typically associated with poultry and dairy cows in the United States, and ST198 is typically associated with human infections acquired in Africa, South Asia, the Middle East and Europe, as well as poultry and cattle in these regions (Foley et al, ; Haley et al, ,; Le Hello et al, ; Raufu et al, ). However, the geographic distinction between these types is not perfect as ST152 has been isolated outside of the Americas and ST198 has been isolated in the Americas (Alikhan et al, ; Kim et al, ).…”

Genome Sequences of Salmonella enterica subsp. enterica Serovar Kentucky Sequence Type 152 Isolated from Dairy Cows in the United States

“…Kentucky ST198 has received the most attention due to the epidemic status of multidrug-resistant strains among humans in Africa, the Middle East, and South Asia, with cases in North America and Europe primarily linked with travel to those regions ( 2 – 6 ). S. Kentucky ST152 is rarely isolated from humans but is frequently isolated from asymptomatic cattle and poultry across the United States ( 7 – 10 ).…”